Hepatitis C-associated osteosclerosis (HCAO) is a rare syndrome characterized by a marked increase in skeletal mass in adults who are infected with the hepatitis C virus. Beyer et al., J. Bone Min. Res., 5:1257-1263 (1990); and Diamond et al., Bone, 19:679-683 (1996). Spine and hip bone mineral densities are elevated as much as two-fold in these affected individuals, who represent the most dramatic example of acquired osteosclerosis in humans. Radiographs show dense bones in the appendicular and axial skeleton, with sparing of the calvarium and facial bones. Biochemical markers of bone formation are usually elevated, and transiliac bone biopsies generally show increased bone formation rates. Nevertheless, osseous tissue from these patients appears histologically to be of good quality with intact lamellar patterns, unlike the abnormal, rapidly remodeling woven bone found in patients with Paget's bone disease.
To date, ten cases of HCAO have been reported. It is apparent, however, that only a small percentage of all patients infected with hepatitis C develop osteosclerosis, since skeletal radiographs of 107 randomly selected hepatitis C infected patients failed to show dense bones. Beyer et al., Am. J. Med., 95:660-662 (1990). Thus, although it is uncertain whether hepatitis C is the causative agent of the skeletal disease, a plausible hypothesis is that either hepatitis C or another parenterally transmitted agent increases hepatic production of a growth factor(s) that stimulate osteoblast function.